The long-term aim is a better understanding of the mechanisms that are responsible for poor hearing in noise by listeners with sensorineural hearing loss. Aim 1 will investigate the hypothesis that the poor performance of hearing-impaired listeners in fluctuating noise is due to an interaction between poor frequency selectivity and reduced speech redundancy. The aim will also investigate a competing hypothesis that such poor performance is due to poor encoding of temporal fine structure cues. Aim 2 investigates the combination of speech or temporal envelope across frequency. We test the hypothesis that poor performance of hearing-impaired listeners in the combination of such information is related to poor frequency selectivity rather than to an essential deficit in processes that are related to the combination of information across different frequency channels. Aim 3 explores issues related to the relationship between frequency selectivity and temporal processing in both hearing-impaired and normal-hearing listeners. One series of experiments in this aim tests the hypothesis that hearing-impaired listeners will show better than normal temporal processing in paradigms where it is more advantageous to base performance on the output of a single, broad auditory filter than to combine information across multiple, narrow auditory filters. In contrast, a second series of experiments uses a novel monaural envelope correlation perception paradigm where it appears that normal-hearing listeners are able to achieve acute temporal processing by combining information across multiple, narrow auditory filters. It is hypothesized that hearing-impaired listeners will not perform better than normal in these conditions, but, instead, may well show a performance deficit. Psychoacoustic studies will use standard, adaptive testing techniques, and speech studies will use a combination of adaptive and fixed block methods. Data will be analyzed using analysis of variance and correlation procedures. The proposed work relates to public health in that the data from the studies on hearing loss will provide information about the effect of sensorineural hearing loss on the ability to understand speech in quiet and in noise. The studies on normal hearing investigate phenomena that are likely to be relevant to the ability of normal and hearing-impaired listeners to process complex sounds such as speech. This project is directly relevant to public health in that it investigates possible forms of hearing disability in adults who have sensorineural hearing loss. The project also investigates hearing processes that underlie the ability to hear signals in background noise. This is relevant to public health because poor hearing in background noise is the most common complaint of patients with sensorineural hearing loss.